The current 2 cell charger shares a charging circuit between both channels - only one channel can be charged at a time. Charging 2 cells simultaneously is actually achieved by switching the charging current between each channel.

What I'd like to see is for each channel to have its own charging circuit so that all channels could be charging independently.

(Maximum charging current of at least 2 amps would also be ideal)

To do this, I think that each channels would have to have proper control independent of the controller - i.e. the controller would just set a DAC line to set the current and the charging circuitry should automatically adjust the PWM to compensate for fluctuating source voltage. (Trying to compensate for fluctuations in the supply voltage with 4 channels turning on and off would be difficult to do quickly enough with the controller)

From a software point of view, it would be nicer if the channels were all independent (with maybe an upper limit on total current across all 4 channels) since it would make things simpler, but if it's going to save a reasonable amount on the cost of the charger, than 2 channels would be a reasonable compromise.

Maybe have the left channel paired with the top and the right paired with the bottom. For maximum charging rates, you then either use the side channels together, or the top and bottom channel together.

I thought one of the advantages of the 2 cell charger was each cell was charged separately. Why would it be a good idea to give up that concept on a 4 cell charger? I know cost is driving at least some of such decisions but how much might a 4 cell charger cost with 4 independent chargers vs. 2 two-cell circuits?

My interest in these 'ultimate' chargers is because I want the best available even though I already have some pretty good ones (including a Maha MH-C401FS). As a result I'm prepared to be spending a bit more than usual to get more performance. Don't scrimp on design just to compete on cost with chargers that already exist on the market.

Or have I totally missed the point of this topic?

Russel

fyi, I'm not conversant on state of the art although I use to be an electronics tech 30 years ago. ex-USAF weather equipment repair, ex IBM CE mainframe, old radio ham.

With the 2 cell charger, there is only one actual charging circuit, so only one cell is ever being charged at any given instant. Charging 2 cells together is done by alternating between the channels. The same would apply to the 4 channel charger, so each charging channel would be shared between 2 cells. Each cell would still be independently monitored, so it's really not much different to two 2 channel chargers working on the same board.

I've actually been thinking about this topic a little recently and I'm swinging back to wanting 4 full charging circuits:

Not only would it make it easier from a software point of view, but it would allow for faster charging when charging 4 cells at the same time. Even when not charging at maximum charging rates, having 4 separate charging circuits would mean that instead of having to charge at double the rate for half the time, the charger would be charging at a lower rate pretty much all of the time. Doubling the charge rate at a 50% duty cycle leads to higher resistive losses in the cells (Double in fact!) compared to maintaining a lower rate all of the time.

Although it would undoubtedly add to the cost of the charger, I think it would be worthwhile - the cost of the charger is already going to be significantly higher than something like the C9000, so I think that those looking to spend this much would be willing to pay a bit more for something that is better in every regard rather than being a step backwards in some regards. I know that I'd prefer to spend say $170 on a full 4 channel charger design compared to $150 for a charger with reduced capabilities.

Ultimately though, Paul is the hardware guy, so it's his decision in the end - we can only tell him what we would prefer. The more people that chip in and say that they'd prefer to pay the extra, the higher the chances are that he'll go that way.

RLBrooks wrote:I thought one of the advantages of the 2 cell charger was each cell was charged separately.

Yes they are charged independently even though they share the same charging circuit. In chargers where they are charged in pairs the cells are electrically connected such that it is impossible to charge one cell without also charging the other (same goes with stopping the charge). In this charger the cells are charged by the same charging circuit but it is switched between them. This means that you can stop and start each cell completely independently of each other. It also means you can charge them at different rates. The catch with doing the electronics this way is that the maximum charge current you can charge a cell at (and still charge both slots simultaneously) is 1/2 the maxim that the electronics can deliver (because it is switching between them). For the highest current setting, one cell actually waits while the other is completely charged before it gets its turn. In older electronics that had 7 segment displays (http://en.wikipedia.org/wiki/Seven-segment_display, like alarm clocks and microwave ovens) there is often more than 1 digit however the electronics are usually only controlling only 1 at a time and then switching between them really fast. Each digit displays totally independently even though it is still only being driven by the same set of electronics. Does this make sense?

Paul.Allen wrote:Each digit displays totally independently even though it is still only being driven by the same set of electronics. Does this make sense?

Yes, I understand those circuits and it is useful for a display because the eye can't see the flicker so there is no loss of function. However time slicing charging across multiple batteries means there must be some loss of charge performance during periods the charger is servicing the other battery(s).